Devices for stream feeding of sheets onto a stack are usually used downstream of a crosscutter, but it also is possible to use such devices downstream of printing presses.
A device by means of which sheets of different lengths can be deposited is known from DE-OS 38 12 685. In this braking mechanism for sheet deposition, successively arranged sheets, or layers of sheets are fed with a delivery speed to a slower running conveyor, so that the sheets overlap. This slightly scaled layer stream runs through a braking gap, which reinforces the scale arrangement. The braking gap is formed by a braking member slidable in travel direction above and below the conveyor.
The drawback of this device is that in the braking gap due to the pressure applied over the very short span the danger of impressions on the sheets is especially high. Particularly, in the case of sensitive materials, e.g. labels, such impressions can hardly be avoided. In addition, the conveyors themselves with their lower and upper conveyor belts can easily lead to impressions. Besides, braking mechanisms with conveyor belts have a high manufacturing cost and, due to their large extension in the travel direction, also have big space requirements.
A further device with conveyor belts is known from the DE-OS 41 19 511. This device is equipped with clamping elements for braking the sheets, which again leads to impressions, particularly in the case of sensitive materials.
From German Patents 23 48 320, 25 32 880, 26 15 864 and 28 41 658 devices for the stream feeding of sheets onto a stack are known, wherein suspension rails are used for conveying the sheets.
By means of suspension rails the sheets are transported on an air cushion without the danger of impressions. Also in their braking devices, suction rollers or suction rails there is substantially less danger of impressions when compared to a braking gap or clamping elements. These devices have a more compact construction than the devices having conveyor belts. However, they have the disadvantage that they can be used only for sheets of the same length.
In the species-establishing device described in German Patent 28 41 658 the braking device is built as a swingable suction rail, whereby the drive of a deflection device is synchronized with the drive of the suction rail. This device is suitable only for long sheets having the same length. An eventual refitting of the drives for a changed sheet length is difficult, if not downright impossible. Besides with these drives it is not possible to quickly revert the suction rail to its initial position, in order to brake short sheets delivered at high speed.